The present invention relates to a scanning line interpolation apparatus and method for interpolating pixels or lines such as scanning lines of, e.g., a television image.
A conventional scanning line interpolation apparatus and method are generally applied to television devices. The scanning line interpolation schemes used in displaying images on television devices are mainly classified into three-dimensional processing and two-dimensional processing.
In general conventional three-dimensional processing, motion detection is performed using the pixel difference between adjacent frames in a motion adaptive scanning line interpolation scheme. The pixel data of the previous field is mixed with the pixel data obtained by averaging the pixel data on the upper and lower scanning lines of the current field in accordance with a degree of motion to obtain an interpolated signal, thereby properly performing scanning line interpolation for both still and moving images.
General conventional two-dimensional processing includes an average value scanning line interpolation scheme for performing interpolation using, as an interpolated scanning line, a value obtained by averaging upper and lower scanning lines in a field, and a simple overwrite scanning line interpolation scheme for simply scanning the same scanning line twice.
Japanese Patent Laid-Open No. 1-194693 entitled as a "motion adaptive scanning line interpolation method" is proposed as individual prior art 1. According to prior art 1, a one-frame difference is compared with a two-frame difference in motion coefficient detection by a motion coefficient generator having characteristics in which a motion coefficient decreases with an increase in level of a signal difference detected by an interframe difference. A smaller motion coefficient is employed. This implies that a larger motion is employed.
The motion coefficients obtained as described above are compared for three adjacent fields to employ a minimum value. The maximum motion is detected in the motion detection range using the one- and two-frame differences of the three adjacent fields. Scanning line interpolation of the current field is performed using this maximum motion. To employ the maximum motion is to employ a large weight in the bilinear data of the current field.
With the above arrangement, the bilinear data is employed as interpolated data in a higher degree as compared with a degree of motion. A slight decrease in resolution occurs accordingly, but an after image effect by inappropriate interpolation of previous field data can be prevented in advance. Therefore, the total image quality can be improved.
Japanese Patent Laid-Open No. 7-327148 entitled as a "line interpolation method and apparatus" is proposed as individual prior art 2. According to prior art 2, six pixels around a pixel of interest are calculated to express them in at least one of the luminance, hue, and saturation components. A pixel pair correlated with each other is selected from three pixel pairs, i.e., the pair of upper and lower pixels, the pair of upper right pixel and lower left pixel, and the pair of upper left pixel and lower right pixel with respect to the pixel of interest. The signal value of the selected pixel pair is changed to the signal value of the pixel of interest for each component. If no correlation is established in any one of the pixel pairs, the average value of the upper and lower pixels is defined as the signal value of the pixel of interest.
With the above arrangement, line interpolation having a higher correlation with the upper and lower lines can be performed. At the same time, interpolation having an importance in correlation for a color image can also be performed. Therefore, an image having a higher image quality can be obtained.
The motion adaptive scanning line interpolation scheme must detect the motion, the circuit scale increases due the presence of a motion detection circuit and an adaptive scanning line interpolation circuit, and the capacity of a memory also increases. The vertical resolution in the average value scanning line interpolation scheme becomes lower than that in interlaced scanning. In the simple overwrite scanning line interpolation scheme, obliquely rendered components become stepped as compared with an original image.
Prior arts 1 and 2 are associated with the motion adaptive scanning line interpolation scheme and the average value scanning line interpolation scheme, respectively. Prior arts 1 and 2 improve the problems and drawbacks of the corresponding schemes.